Carbon nanotubes (CNTs) are tubules of narrow diameter (typically 1-100 nm) made of carbon atoms. CNT's have shown huge potential for applications with distinctive electrical and mechanical properties. The devices based on CNTs are feasible due to their superior material properties. These properties include high aspect ratio, high mechanical strength, chemical stability, and high electrical conductivity. Single wall nanotubes (SWNTS) can be either metallic or semiconducting. Individual SWNT can be used as interconnects as well as a field effect transistor. Combinations of nanotubes can be fabricated as rectifiers or more complex multidimensional structures. Further, the atomic structure of CNTs is associated with high mechanical stiffness as well as great flexibility. For example, carbon nanotubes may be 100 times stronger than steel while their weight is one sixth as much. CNTs have a Young's Modulus of 1.8 TPa and resist deformation remarkably well. Additionally, the CNTs regain their cylindrical and straight shape once the bending strain is released.
One interesting property of CNTs is the cold field emission of electrons. The cold field emission properties of CNTs are attributed to the fact that their aspect ratio (length to diameter) is very high. In addition, the presence of a high concentration of defects modify the electrical resistance and field emission properties of CNTs. Common defects in CNTs include vacancies and non hexagonal carbon rings. The specific combination of such defects may lead to the formation of nanotube junctions and branched nanotubes. These can be present in as-grown CNTs, but controlling their density externally opens a path towards the tuning of the field emission characteristics of the nanotubes.
Additionally, carbon nanotubes (CNTs) are generally formed in a forest type structure in which the tubes are entangled with one another due to Van der Waal forces. These structures can become difficult/impossible to use for a variety of applications due to their inherent structural complexities.